What the part is and where it sits
The Square D / Telemecanique XU9N18NP341WD is an 18 mm tubular photoelectric sensor in the XU9 line, polarized retroreflective class, paired with a reflector to detect objects at up to 2 m along the optical axis. It runs on 12 to 24 VDC, switches a 100 mA load through a 3-wire NPN output that can be wired either normally open or normally closed, and exposes the state on a yellow output LED. The stainless steel barrel carries a 4-pin micro connector on the back, threads straight into a standard 18 mm through-hole, and is rated NEMA 4X/12 with an IP67 seal — which is the envelope that lets it sit in washdown, outdoor, or food-adjacent skids without a separate shroud.
Key ratings and what they govern
Sensing distance is 2 m, with the beam exiting at a 90 deg side look — so the reflector mounts perpendicular to the sensor body, not in line with the cable exit, which keeps the cordset out of the optical path on a conveyor frame. Response time is 1 ms on and off, with a 500 Hz operating frequency, so the sensor can resolve objects on lines running well under typical conveyor indexing speeds without aliasing. Operating temperature spans -13 to 131 DEG F, covering cold-storage docks and most washdown ambient without derating; load current is capped at 100 MILLIAMPERE, which is the figure that decides whether it drives a relay coil directly or has to feed a PLC input card instead. Approvals on the rating plate are UL, CSA, and CE, so the same part ships into North American and European panels without a separate compliance review.
Use class and where it lands in a panel
Polarized retroreflective tubular sensors of this class are used to detect bottles, cartons, totes, and printed web at case-packers, labelers, and pallet exits, where the retroreflector doubles as the far-side reference and ignores small specular reflections from shrink-wrap or polished metal that would confuse a standard retroreflective pair. The light/dark operating mode is selectable on the body, so the same SKU covers both presence and absence logic at commissioning without a re-order.
Same-class peers and the actual decision they drive
The closest same-form-factor siblings are the XUB9BPAWM12 (PNP, normally open) and XUB9BPBWM12 (PNP, normally closed) — same 18 mm barrel, same 2 m polarized retroreflective range, same 1 ms response and 500 Hz frequency, but PNP sourcing outputs and a nickel-plated brass housing rather than stainless steel. The XU9N18NP341WD does not drop into a panel specified around a PNP sensor without rewiring: NPN sinks current into a load tied to the positive rail, PNP sources current into a load tied to ground, and the PLC input card or relay common on the original drawing will not match. For a washdown or outdoor skid that needed the stainless body in the first place, a PNP swap also means giving up the corrosion resistance — the housing material is part of the original spec, not a styling choice.
Sourcing posture and lifecycle
Lifecycle is recorded as current, so the XU9N18NP341WD is ordered through the standard Telemecanique/Square D channel against an RFQ, with the 4-pin micro M12 cordset specified separately on the BOM line. Approval marking on the rating plate covers UL, CSA, and CE, which is the documentation pack a supplier-quality reviewer will want to see on first article.